Alien 4 Scheduler; sched: Do not block when waiting to free old root domain
Instead of calling synchronize_sched(), directly invoke
call_rcu_sched() which will not block the cpu hotplug
operation but will call free_rootdomain when the rcu
process is complete. This is safe because the root
domains are allocated dynamically so any new readers
will have pointers to the new data and the new data
does not overwrite the old data.

This is a partial backport from 3.0.0 kernel.
I did not backport the dynamic allocation of the sched
domain and sched group data structures.  This would
require inclusion of 10 other patches and would not be
stable.